In recent years, for example, a projection type liquid crystal display apparatus using a spatial modulation device typified by a liquid crystal panel as an optical switching device, and magnifying and projecting an image on the liquid crystal panel on a screen by a projection optical system such as a liquid crystal projector or the like has been widely used. As the liquid crystal display apparatus of this kind, a single-panel system comprising one liquid crystal panel including three color filters of B (blue), R (red) and G (green), and a three-panel system comprising three monochrome liquid crystal panels for optical paths of B (blue), R (red) and G (green) are cited.
As a light source of an illumination optical system in such a projection type liquid crystal display apparatus, a metal halide lamp, a super high pressure mercury lamp or the like which has a continuous emission spectrum throughout the wavelength range of visible light is generally used.
FIG. 10 shows an emission spectrum of the super high pressure mercury lamp. As shown in FIG. 10, the emission spectrum of the super high pressure mercury lamp contains a few energy peaks. In the emission spectrum, light having an energy peak PB in a wavelength range of 400 nm to 480 nm is used as blue light, and light having an energy peak PG in a wavelength range of 490 nm to 550 nm is used as green light. Further, light in a wavelength range of 620 nm to 700 nm is used as red light.
However, as shown in FIG. 10, in such a super high pressure mercury lamp, compared to blue light and green light, the relative intensity of red light is considerably insufficient. Due to the insufficiency of a red light component, the white balance of a projected image finally obtained tends toward green and blue, so favorable color rendering properties cannot be obtained. Therefore, the intensities of a green light component and a blue light component are unavoidably reduced so as to adjust the white balance, thereby favorable color rendering properties are obtained. However, in such a method, the whole illuminance declines, thereby resulting in the occurrence of such a problem that the brightness of the projected image cannot be sufficiently obtained.
Further, the emission spectrum in FIG. 10 contains a yellow light component or an orange light component having a higher energy peak PY than the energy level of a red waveband in a wavelength range of around 580 nm. The presence of the yellow component or the orange component causes a problem in the color rendering properties of the projected image, such as changing the original color of the projected image which should be red to orange, or changing the original color of the projected image which should be green to yellow-green. In the case where the metal halide lamp is used, the problem occurs in a like manner.
In view of the foregoing, it is an object of the invention to provide an illumination optical system having superior color rendering properties while ensuring sufficient illuminance, an image display apparatus comprising such an illumination optical system and a spatial modulation device illuminated by the illumination optical system, and a method of illuminating such a spatial modulation device.